Transmitter circuit with power detection

ABSTRACT

A transmitter circuit includes an amplifier configured to output a radio frequency (RF) signal on an output node, a power detection circuit coupled with the output node and configured to generate an output voltage having a first component based on a power level of the RF signal, and a reference voltage generator configured to generate a reference voltage. A comparator is configured to receive the output voltage and the reference voltage, an analog-to-digital converter (ADC) is coupled between the comparator and the amplifier, and the amplifier is configured to adjust the power level of the RF signal responsive to an output of the ADC.

PRIORITY CLAIM

The present application is a divisional of U.S. application Ser. No. 15/682,918, filed Aug. 22, 2017, which claims the priority of U.S. Provisional Application No. 62/427,592, filed Nov. 29, 2016, which are incorporated herein by reference in their entireties.

BACKGROUND

Radio frequency (RF) transmitters often are designed to meet industry standards that facilitate desired communications and avoid undesired interference by maintaining compatibility with other devices. To ensure such compatibility, industry standards typically include provisions directed to transmitter power levels.

In some RF transmitter circuit applications, an output stage includes a power amplifier that is part of an integrated circuit (IC) chip. Transmitter components can include additional IC circuits as well as components such as antennae located externally to the IC chip.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a diagram of a transmitter circuit, in accordance with some embodiments.

FIG. 2 is a diagram of a power detection circuit, in accordance with some embodiments.

FIG. 3 is a diagram of a reference voltage circuit, in accordance with some embodiments.

FIG. 4 is a diagram of a comparator circuit, in accordance with some embodiments.

FIG. 5 is a timing diagram of voltage and current signals at various nodes of the power detection circuit of FIG. 2, in accordance with some embodiments.

FIG. 6 is a diagram of a transfer function of the power detection circuit of FIG. 2, in accordance with some embodiments.

FIGS. 7A and 7B are timing diagrams of voltage signals at various nodes of the transmitter circuit of FIG. 1, in accordance with some embodiments.

FIG. 8 is a flowchart of a method of detecting a power level of an RF signal, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components, values, operations, materials, arrangements, or the like, are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. Other components, values, operations, materials, arrangements, or the like, are contemplated. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

In some embodiments, a transmitter circuit includes an amplifier that outputs an RF signal on an output node, a power detection circuit coupled with the output node, a reference voltage generator, a comparator that receives an output voltage of the power detection circuit and a reference voltage of the reference voltage generator, and an ADC coupled between the comparator and the amplifier. The power detection circuit generates the output voltage having a first component based on a DC bias voltage and a second component based on a power level of the RF signal. The reference voltage generator generates the reference voltage based on the DC bias voltage, and the amplifier adjusts the power level of the RF signal responsive to an output of the ADC.

FIG. 1 is a diagram of a transmitter circuit 100, in accordance with some embodiments. Transmitter circuit 100 includes an amplifier 110, a power detection circuit 120, a reference voltage generator 130, a comparator 140, and an analog-to-digital converter (ADC) 150. Amplifier 110 is electrically coupled to power detection circuit 120 by a node 115, power detection circuit 120 is electrically coupled to comparator 140 by a node 125, reference voltage generator 130 is electrically coupled to comparator 140 by a node 135, comparator 140 is electrically coupled to ADC 150 by a node 145, and ADC 150 is electrically coupled to amplifier 110 by a signal path 155.

In some embodiments, transmitter circuit 100 is a component of an RF transmitter. In some embodiments, transmitter circuit 100 is a component of an RF transmitter having an operating frequency from 2.2 gigahertz (GHz) to 2.6 GHz. In some embodiments, transmitter circuit 100 is a component of an RF transmitter having an operating frequency from 5.6 GHz to 6.0 GHz.

In some embodiments, transmitter circuit 100 is a component of an RF transmitter conforming to a wireless network standard. In some embodiments, transmitter circuit 100 is a component of an RF transmitter conforming to a Bluetooth standard.

Amplifier 110 is an RF power amplifier configured to receive one or more input signals (not shown) on one or more input terminals (not shown) and output a signal RFOUT on node 115. Amplifier 110 is configured to generate signal RFOUT by increasing an amplitude of the one or more input signals by a gain having a gain level, and to adjust the gain level in response to a plurality of bits n received on signal path 155.

In some embodiments, amplifier 110 is configured to generate signal RFOUT by increasing the amplitude of an input signal relative to a ground or other reference level. In some embodiments, amplifier 110 is configured to generate signal RFOUT by increasing the amplitude of a differential input signal.

By adjusting the gain level in response to plurality of bits n, amplifier 110 is capable of outputting signal RFOUT having a predetermined power level controlled by plurality of bits n. In some embodiments, plurality of bits n ranges from a lowest value to a highest value, and amplifier 110 is configured to adjust the gain level inversely to the value of plurality of bits n. In some embodiments, plurality of bits n ranges from a lowest value to a highest value, and amplifier 110 is configured to adjust the gain level proportionally to the value of plurality of bits n.

In some embodiments, amplifier 110 is configured to respond to plurality of bits n on signal path 155 having a number ranging from 4 bits to 6 bits. In some embodiments, amplifier 110 is configured to respond to plurality of bits n on signal path 155 having fewer than 4 bits. In some embodiments, amplifier 110 is configured to respond to plurality of bits n on signal path 155 having greater than 6 bits.

In some embodiments, amplifier 110 is configured to respond to plurality of bits n received in series. In some embodiments, signal path 155 includes more than one conductive path, and amplifier 110 is configured to respond to plurality of bits n received in parallel.

Power detection circuit 120 is configured to receive signal RFOUT on node 115 and to output a voltage VRF on node 125. Power detection circuit 120 is configured to generate voltage VRF having a direct current (DC) voltage level that includes a first component summed with a second component. In some embodiments, voltage VRF includes one or more alternating current (AC) or other time-varying components that are small relative to the first and second components of the DC voltage level.

The first component of the DC voltage level corresponds to a predetermined voltage level, and the second component of the DC voltage level varies based on an amplitude of signal RFOUT.

In some embodiments, power detection circuit 120 is configured to generate the second component of the DC voltage level having a magnitude that increases with respect to an increasing amplitude, or power level, of signal RFOUT. In some embodiments, power detection circuit 120 is configured to generate the second component of the DC voltage level having a magnitude that decreases with respect to an increasing amplitude, or power level, of signal RFOUT.

Reference voltage generator 130 is configured to generate a reference voltage VREF and output reference voltage VREF on node 135. Reference voltage generator 130 is configured to generate reference voltage VREF having a DC voltage level corresponding to the first component of the DC voltage level of voltage VRF.

In some embodiments, reference voltage generator 130 is configured to generate reference voltage VREF having a DC voltage level equal to the first component of the DC voltage level of voltage VRF. In some embodiments, reference voltage generator 130 is configured to generate reference voltage VREF having a DC voltage level equal to the first component of the DC voltage level of voltage VRF plus or minus an offset value. In some embodiments, reference voltage generator 130 is configured to generate reference voltage VREF having a DC voltage level proportional to the first component of the DC voltage level of voltage VRF.

Comparator 140 is configured to receive voltage VRF on node 125, receive reference voltage VREF on node 135, generate a voltage VCMP based on a difference between voltage VRF and reference voltage VREF, and output voltage VCMP on node 145. In some embodiments, comparator 140 is configured to generate voltage VCMP equal to a difference between voltage VRF and reference voltage VREF.

Because reference voltage VREF corresponds to the first component of the DC level of voltage VRF, and voltage VCMP is based on the difference between voltage VRF and reference voltage VREF, voltage VCMP has a magnitude that varies based on the second component of the DC level of voltage VRF, and therefore based on the amplitude, or power level, of signal RFOUT.

ADC 150 is configured to receive voltage VCMP on node 145 and generate plurality of bits n on signal path 155 based on voltage VCMP. In some embodiments, ADC 150 is configured to generate plurality of bits n ranging from a lowest value to a highest value, with the value varying proportionally to a value of voltage VCMP. In some embodiments, ADC 150 is configured to generate plurality of bits n ranging from a lowest value to a highest value, with the value varying inversely to a value of voltage VCMP. In some embodiments, ADC 150 is a successive approximation register (SAR) ADC.

In some embodiments, ADC 150 is configured to generate plurality of bits non signal path 155 having a number ranging from 4 bits to 6 bits. In some embodiments, ADC 150 is configured to generate plurality of bits n on signal path 155 having fewer than 4 bits. In some embodiments, ADC 150 is configured to generate plurality of bits n on signal path 155 having greater than 6 bits.

In some embodiments, ADC 150 is configured to generate plurality of bits non signal path 155 in series. In some embodiments in which signal path 155 includes more than one conductive path, ADC 150 is configured to generate plurality of bits non signal path 155 in parallel.

In operation, plurality of bits n, based on voltage VCMP, provide feedback to amplifier 110 such that adjustments to the gain level of amplifier 110 maintain a predetermined power level of signal RFOUT. In some embodiments, in operation, amplifier 110 increases the gain level in response to plurality of bits n having one or more first values and decreases the gain level in response to plurality of bits n having one or more second values different from the one or more first values. In some embodiments, in operation, amplifier 110 adjusts the gain level in response to plurality of bits n having one or more first values and maintains a previous gain level in response to plurality of bits n having one or more second values different from the one or more first values.

In some embodiments, in operation, amplifier 110 sets the gain level to a level of a plurality of levels, each level corresponding to a value of a plurality of values of plurality of bits n.

By this configuration, transmitter circuit 100 is capable of compensating for process and temperature variations in an output power of amplifier 110. The comparator-based architecture of transmitter circuit 100 enables process and temperature variation compensation with lower power and smaller area requirements compared to other approaches for making amplifier gain adjustments.

In some embodiments, amplifier 110, power detection circuit 120, reference voltage generator 130, comparator 140, and ADC 150 are components of a single IC chip, and transmitter circuit 100 uses fewer off-chip components and less space than are required using other approaches for making amplifier gain adjustments.

FIG. 2 is a diagram of a power detection circuit 200, in accordance with some embodiments. Power detection circuit 200 is usable as power detection circuit 120, described above with respect to transmitter circuit 100 and FIG. 1. Power detection circuit 200 includes devices C1, R1, M1, M2, M3, and C2. Power detection circuit 200 also includes an input node IN configured to receive an RF signal RFIN, and an output node OUT. In some embodiments, RF signal RFIN is RF signal RFOUT, input node IN is node 115, and output node OUT is node 125, each described above with respect to transmitter circuit 100 and FIG. 1.

Device C1 is coupled between input node IN and an internal node INT1. Device R1 is coupled between an input node BIAS and internal node INT1. Device M1 is coupled between internal node INT1, a signal node CLK, and a ground node GND. Device M2 is coupled between internal node INT1, a power node PWR, and output node OUT. Device M3 is coupled between output node OUT, signal node CLK, and ground node GND. Device C2 is coupled between output node OUT and ground node GND.

Power detection circuit 200 is configured to switch between a first mode of operation and a second mode of operation responsive to a signal ϕCLK on signal node CLK, as described below.

Device C1 is a circuit component configured to receive RF signal RFIN on input node IN and transfer at least a portion of RF signal RFIN to internal node INT1 by capacitively coupling input node IN to internal node INT1.

In the embodiment depicted in FIG. 2, device C1 is a capacitive element. In some embodiments, device C1 is a capacitor. In some embodiments, device C1 is a transistor or other suitable device configured to transfer at least a portion of RF signal RFIN from input node IN to internal node INT1.

Device R1 is a circuit component configured to transfer at least a portion of a DC voltage VBIAS from input BIAS to internal node INT1 by resistively coupling input node BIAS to internal node INT1. In the embodiment depicted in FIG. 2, device R1 is a resistive element. In some embodiments, device R1 is a resistor. In some embodiments, device R1 is a transistor or other suitable device configured to transfer at least a portion of DC voltage VBIAS from input node BIAS to internal node INT1.

Device M1 is a circuit component configured to selectively couple internal node INT1 to ground node GND, responsive to signal ϕCLK on signal node CLK.

In the first mode of operation, device M1 responds to a first logical state of signal ϕCLK by coupling internal node INT1 to ground node GND with a low-impedance path for both AC and DC components of voltage VIN. In the second mode of operation, device M1 responds to a second logical state of signal ϕCLK different from the first state by capacitively coupling internal node INT1 to ground node GND, thereby providing a high-resistance path for a DC component of voltage VIN.

In the embodiment depicted in FIG. 2, device M1 is an n-type metal oxide semiconductor (NMOS) transistor configured to operate in the first mode in response to signal ϕCLK having a high voltage value corresponding to the first logical state and to operate in the second mode in response to signal ϕCLK having a low voltage value corresponding to the second logical state. In some embodiments, device M1 is a p-type metal oxide semiconductor (PMOS) transistor or other suitable device configured to selectively operate in first and second modes in response to signal ϕCLK, as described above.

By the configuration of devices R1 and M1, DC voltage VBIAS is divided to generate a DC node voltage component of voltage VIN on internal node INT1. In the first mode of operation, because device M1 provides a low-resistance path between internal node INT1 and ground node GND, the DC node voltage component of voltage VIN has a value at or near a ground voltage level on ground node GND.

In the second mode of operation, because device M1 provides a high-resistance path between internal node INT1 and ground node GND, the DC node voltage has a value between a value of DC voltage VBIAS and the ground voltage level. The value of the DC node voltage component of voltage VIN is determined by the relative resistance values of devices R1 and M1 while operating in the second mode of operation.

By the configuration of devices C1 and M1, RF signal RFIN is divided to generate an RF component of voltage VIN on internal node INT1. In the first mode of operation, because device M1 provides a low-impedance path between internal node INT1 and ground node GND, the RF component of voltage VIN has a value at or near the ground voltage level on ground node GND.

In the second mode of operation, because device M1 capacitively couples internal node INT1 to ground node GND, devices C1 and M1 divide RF signal RFIN to generate an RF modulation signal as the AC component of voltage VIN. The RF modulation signal has a magnitude that is a fraction of the magnitude of RF signal RFIN. The ratio of the magnitude of the RF modulation signal to the magnitude of RF signal RFIN is determined by the relative capacitance values of devices C1 and M1 while operating in the second operating mode.

Devices C1, R1, and M1 are thereby configured to generate voltage VIN having DC and AC components at or near the ground voltage level in the first mode of operation, and to generate voltage VIN in the second mode of operation having a DC node voltage that is a fraction of DC voltage VBIAS and an RF modulation signal that is a fraction of RF signal RFIN.

The fractional value of the DC node voltage results from the voltage divider configuration of a resistance value RR1 of device R1 and a resistance value RM1 of the high-resistance path of device M1 while operating in the second mode of operation, and is therefore determined by the equation:

DC node voltage value=VBIAS×RM1/(RM1+RR1).  (1)

The fractional value of the RF modulation signal results from the voltage divider configuration of a capacitance value CC1 of device C1 and a capacitance value CM1 of device M1 while operating in the second mode of operation, and is therefore determined by the equation:

RF modulation signal value=RFIN×CC1/(CM1+CC1).  (2)

Device M2 is a circuit component configured to selectively transfer, or trace, voltage VIN from internal node INT1 to output node OUT. Device M2 is configured to receive a power supply voltage VDD on power node PWR and to selectively output current ID on output node OUT.

In the embodiment depicted in FIG. 2, device M2 is an NMOS transistor configured as a source follower. In some embodiments, device M2 is a PMOS transistor or other suitable device configured to selectively transfer voltage VIN from internal node INT1 to output node OUT and to selectively output current ID on output node OUT.

Device M3 is a circuit component configured to selectively couple output node OUT to ground node GND, responsive to signal ϕCLK on signal node CLK.

In the first mode of operation, device M3 responds to the first logical state of signal ϕCLK by coupling output node OUT to ground node GND with a low-impedance AC and DC path. In the second mode of operation, device M3 responds to the second logical state of signal ϕCLK by capacitively coupling output node OUT to ground node GND, thereby providing a high-resistance path for the DC node voltage component of voltage VRF on output node OUT. Device M3 is configured so that, in the second mode of operation, the capacitive coupling between output node OUT and ground node GND is asymmetrical such that the RF modulation signal component of voltage VRF is rectified.

In the embodiment depicted in FIG. 2, device M3 is an NMOS transistor configured to operate in the first mode in response to signal ϕCLK having a high voltage value corresponding to the first logical state and to operate in the second mode in response to signal ϕCLK having a low voltage value corresponding to the second logical state. In some embodiments, device M3 is a PMOS transistor or other suitable device configured to selectively operate in first and second modes in response to signal ϕCLK, as described above.

Device C2 is a circuit component configured to capacitively couple output node OUT to ground node GND. In the embodiment depicted in FIG. 2, device C2 is a capacitive element. In some embodiments, device C2 is a capacitor. In some embodiments, device C2 is a transistor or other suitable device configured to capacitively couple output node OUT to ground node GND.

In the first mode of operation, voltage VIN having DC and AC components at or near the ground voltage level, as described above, causes device M2 to be switched off and current ID to be at or near zero. Because device M3 is also configured to couple output node OUT to ground node GND with a low-impedance AC and DC path in the first mode of operation, voltage VRF is generated on output node OUT having a value at or near the ground voltage level.

In the second mode of operation, because device M2 is configured as a source follower and both of devices M3 and C2 are configured as high-resistance DC paths, the DC node voltage component of voltage VIN is transferred to output node OUT to generate a first DC component of voltage VRF.

In the second mode of operation, devices M3 and C2 act to rectify the RF modulation signal component of voltage VIN that is transferred from internal node INT1 to output node OUT. The RF modulation signal component of voltage VIN on internal node INT1 is therefore transferred to output node OUT as a second DC component of voltage VRF.

In the second mode of operation, because the RF modulation signal component of voltage VIN is generated by dividing RF signal RFIN, as described above, the magnitude of the second DC component of voltage VRF on output node OUT increases with respect to an increasing magnitude of RF signal RFIN, and decreases with respect to a decreasing magnitude of RF signal RFIN.

Power detection circuit 200 is configured to generate the DC component of voltage VIN by dividing DC voltage VBIAS; a sensitivity of a transfer function of power detection circuit 200 is therefore capable of being adjusted by adjusting the voltage level of DC voltage VBIAS. Because device M3 is switched on in the second mode of operation, power detection circuit 200 is configured to respond to DC voltage VBIAS having a voltage level that ranges from a threshold voltage of device M3 to power supply voltage VDD.

As described above, power detection circuit 200 is configured to generate voltage VRF having a first DC component based on DC voltage VBIAS and a second DC component based on the magnitude, or power level, of RF signal RFIN. Power detection circuit 200 is thereby capable of generating the first and second DC components of voltage VRF for detecting a power level of RF signal RFIN using less power than other approaches for detecting a power level of an RF signal.

FIG. 3 is a diagram of a reference voltage generator 300, in accordance with some embodiments. Reference voltage generator 300 is usable as reference voltage generator 130, described above with respect to transmitter circuit 100 and FIG. 1. Reference voltage generator 300 includes devices R2, M4, M5, M6, and C3. Reference voltage generator 300 also includes an output node REF. In some embodiments, output node REF is node 135 described above with respect to transmitter circuit 100 and FIG. 1.

Device R2 is coupled between input node BIAS and an internal node INT2. Device M4 is coupled between internal node INT2, signal node CLK, and ground node GND. Device M5 is coupled between internal node INT2, power node PWR, and output node REF. Device M6 is coupled between output node REF, signal node CLK, and ground node GND. Device C3 is coupled between output node REF and ground node GND.

Devices R2, M4, M5, M6, and C3 correspond to devices R1, M1, M2, M3, and C2, respectively, of power detection circuit 200, described above with respect to FIG. 2, and reference voltage generator 300 has a configuration that matches the configuration of power detection circuit 200, with the exception of a device that corresponds to device C1 of power detection circuit 200.

Accordingly, reference voltage generator 300 is configured to generate output voltage VREF on output node REF having a voltage level that includes the first DC component of voltage VRF but does not include the second DC component of voltage VRF, described above with respect to power detection circuit 200 and FIG. 2.

Similar to power detection circuit 200, reference voltage generator 300 is configured to switch between a first mode of operation and a second mode of operation responsive to signal ϕCLK on signal node CLK. During the first mode of operation, voltage generator 300 generates voltage VREF on output node REF having a value at or near the ground voltage level. During the second mode of operation, voltage generator 300 generates voltage VREF on output node REF having the value of the first DC component of voltage VRF.

Because both power detection circuit 200 and reference voltage generator 300 are configured to switch between first and second modes of operation responsive to the same signal ϕCLK, power detection circuit 200 and reference voltage generator 300, in operation, switch between first and second modes of operation synchronously.

In some embodiments, at least one of power detection circuit 200 or reference voltage generator 300 is configured to respond to signal ϕCLK being a clock signal. In some embodiments, at least one of power detection circuit 200 or reference voltage generator 300 is configured to respond to signal ϕCLK having a switching frequency of 100 Hertz (Hz) to 1000 Hz. In some embodiments, at least one of power detection circuit 200 or reference voltage generator 300 is configured to respond to signal ϕCLK having a switching frequency below 100 Hz. In some embodiments, at least one of power detection circuit 200 or reference voltage generator 300 is configured to respond to signal ϕCLK having a switching frequency above 1000 Hz.

FIG. 4 is a diagram of a comparator 400, in accordance with some embodiments. Comparator 400 is usable as comparator 140, described above with respect to transmitter circuit 100 and FIG. 1. Comparator 400 includes transistors M1A, M2A, M1B, and M2B coupled between power node PWR, carrying power supply voltage VDD, and a node INT3, and transistor MBIAS coupled between node INT3 and ground node GND, at the ground voltage level.

Comparator 400 also includes an input node INP, an input node INN, and an output node CMPOUT. In some embodiments, input node INP is node 125, input node INN is node 135, and output node CMPOUT is node 145, each described above with respect to transmitter circuit 100 and FIG. 1.

Transistors M2A and M2B are PMOS transistors having source terminals coupled to power node PWR and gate terminals coupled to each other and to a drain terminal of transistor M2A. Transistors M2A and M2B are thereby configured as a current mirror such that, in operation, a current IM2A flowing through transistor M2A has a same value as that of a current IM2B flowing through transistor M2B.

Transistor M1A is an NMOS transistor having a source terminal coupled to node INT3, a drain terminal coupled to the drain terminal of transistor M2A, and a gate terminal coupled to node INP carrying voltage VRF. Transistor M1A is thereby configured in series with transistor M2A such that, in operation, current IM2A flows through transistor M1A.

Transistor M1B is an NMOS transistor having a source terminal coupled to node INT3, a drain terminal coupled to the drain terminal of transistor M2B and node CMPOUT, and a gate terminal coupled to node INN carrying voltage VREF. Node CMPOUT is configured so that, in operation, current on node CMPOUT is not significant. Transistor M1B is thereby configured in series with transistor M2B such that, in operation, substantially all of current IM2B flows through transistor M1B.

Because current IM2A is mirrored to current IM2B, in operation, currents through transistors M1A and M1B are the same. In operation, voltage VRF at the gate terminal of transistor M1A, by controlling current flow through transistor M1A, also controls current flow through transistor M1B.

In operation, transistor M1B is controlled both by voltage VREF at the gate terminal of transistor M1B and by voltage VRF at the gate terminal of transistor M1A. By the configuration of transistors M1A and M1B, in operation, a voltage drop across the drain and source terminals of transistor M1B increases as voltage VRF increases relative to voltage VREF and decreases as voltage VRF decreases relative to voltage VREF. Thus, transistors M1A and M1B are referred to as a differential pair.

Transistor MBIAS is an NMOS transistor having a drain terminal coupled to node INT3, a source terminal coupled to ground node GND, and a gate terminal coupled to node BIAS carrying DC voltage VBIAS. In operation, a voltage on node INT3 relative to the ground voltage level is controlled by a value of DC voltage VBIAS at the gate terminal of transistor MBIAS.

Voltage VCMP on node CMPOUT is the sum of the voltage drop across transistor M1B and the voltage on node INT3. For a given value of DC voltage VBIAS, voltage VCMP is controlled by the differential values of voltages VRF and VREF. Comparator 400 is thereby configured as an amplifier such that, in operation, comparator 400 receives voltage VRF on node INP, receives voltage VREF on node INN, generates voltage VCMP based on voltage VREF subtracted from voltage VRF, and outputs voltage VCMP on output node CMPOUT.

Comparator 400 is configured to receive DC voltage VBIAS on node BIAS and to adjust a sensitivity of the differential pair of transistors M1A and M1B to voltages VRF and VREF. In operation, a sufficiently large value of DC voltage VBIAS, e.g., VDD, causes transistor MBIAS to be fully on such that the voltage on node INT3 is near the ground voltage level. As DC voltage VBIAS decreases in value, the voltage on node INT3 and the source terminals of transistors M1A and M1B increases. Because transistors M1A and M1B are controlled by voltages VRF and VREF as discussed above, increasing the voltage on node INT3 increases the sensitivity of transistors M1A and M1B to changes in the values of voltages VRF and VREF at the gate terminals of transistors M1A and M1B.

In addition to comparator 400, both power detection circuit 200 and reference voltage generator 300 are configured to receive DC voltage VBIAS, as discussed above. In some embodiments in which transmitter circuit 100 includes power detection circuit 200, reference voltage generator 300, and comparator 440, transmitter circuit 100 is thereby configured to, in operation, adjust an overall sensitivity to the power level of signal RFOUT.

FIG. 5 is a timing diagram of voltage and current signals at various nodes of power detection circuit 200, in accordance with some embodiments. FIG. 5 depicts voltages VIN and VRF, current ID, and signal ϕCLK, described above with respect to detection circuit 200 and FIG. 2.

At a time t1, signal ϕCLK switches from a high logical level to a low logical level, and, at a time t2, signal ϕCLK switches from the low logical level to the high logical level.

At time t1, voltage VIN rises asymptotically from a value at or near the ground voltage level to a second value that includes the RF modulation signal superimposed on the DC node voltage component of voltage VIN, as described above. At time t2, voltage VIN returns to the value at or near the ground voltage level.

At time t1, voltage VRF rises asymptotically from a value at or near the ground voltage level to a second value that includes the first DC component traced from the DC node voltage component of voltage VIN and the second DC component generated from the rectified RF modulation signal on node INT1, as described above. At time t2, voltage VRF returns to the value at or near the ground voltage level.

At time t1, current ID increases transiently as output node OUT is charged to the second value of voltage VRF, then decays to a value that essentially includes an RF component having an average at or near the ground voltage level.

FIG. 6 is a diagram of a transfer function of power detection circuit 200, in accordance with some embodiments. FIG. 6 depicts voltage VRF as a function of the amplitude of RF signal RFIN, described above with respect to detection circuit 200 and FIG. 2. In the embodiment depicted in FIG. 6, voltage VRF increases linearly with respect to an increasing amplitude of RF signal RFIN.

FIGS. 7A and 7B are timing diagrams of voltage signals at various nodes of transmitter circuit 100, in accordance with some embodiments. Each of FIGS. 7A and 7B depicts voltages VIN, VRF, VREF, and VCMP, and signal ϕCLK, described above with respect to transmitter circuit 100 and FIG. 1. FIG. 7A depicts a first case in which signal RFOUT has a first amplitude, and FIG. 7B depicts a second case in which signal RFOUT has a second amplitude larger than the first amplitude.

In both cases, between time t1, at which point signal ϕCLK switches from the high logical level to the low logical level, and time t2, at which point signal ϕCLK switches from the low logical level to the high logical level, each of signals VIN, VRF, and VREF rises asymptotically to a final value.

In response to the relative magnitudes of signal RFOUT, the RF component of voltage VIN depicted in FIG. 7A is smaller than the RF component of voltage VIN depicted in FIG. 7B. The DC value of voltage VRF is accordingly smaller in the first case depicted in FIG. 7A as compared to the second case depicted in FIG. 7B. Because voltage VREF is independent of the magnitude of signal RFOUT, voltage VREF is unchanged in the depictions of FIGS. 7A and 7B.

Because of the increase in value of voltage VRF in response to the increased amplitude of signal RFOUT, the value of voltage VCMP in the second case, depicted in FIG. 7B, is larger than the value of VCMP in the first case, depicted in FIG. 7A.

In operation, plurality of bits n generated by ADC 150 from voltage VCMP therefore represent the relative magnitude of signal RFOUT, and are used to make gain adjustments to amplifier 110 accordingly.

As described above with respect to power detection circuit 200 and FIG. 5, current ID has an average value at or near the ground reference value while outputting voltage VRF indicative of the power of signal RFOUT. As described above with respect to comparator 400 and FIGS. 7A and 7B, voltages VRF and VREF are received at high-impedance gate terminals of comparator 400 while outputting voltage VCMP indicative of the power of signal RFOUT.

By including power detection circuit 200, transmitter circuit 100 is capable of generating an indication of the amplitude of signal RFOUT while using current ID having a small value, thereby operating at a low power level. By including similarly configured reference voltage generator 300, transmitter circuit 100 is capable of generating a reference voltage while operating at a low power level. Transmitter circuit 100 is thereby configured to calibrate the power of output signal RFOUT using less power and DC current than are required in other RF signal calibration approaches. In some embodiments, transmitter circuit 100 is configured to calibrate signal RFOUT using a DC current that ranges from 50 microamperes (μA) to 100 μA.

In some embodiments, because power detection circuit 200 and reference voltage generator 300 are configured to operate in a first mode of operation in which voltages VRF and VREF are generated having values at or near the ground voltage level, power consumption averaged over the first and second modes of operation is further reduced in comparison to other approaches.

FIG. 8 is a flowchart of a method 800 of method of detecting a power level of an RF signal, in accordance with one or more embodiments. In some embodiments, method 800 is implemented to detect a power level of signal RFOUT of transmitter circuit 100, described above with respect to FIG. 1.

In some embodiments, operations in addition to those depicted in FIG. 8 are performed before, between, and/or after the operations depicted in FIG. 8. In some embodiments, the operations depicted in FIG. 8 are performed in an order other than the order depicted in FIG. 8.

At operation 810, in some embodiments, an RF signal is generated using an amplifier. The RF signal has an amplitude that corresponds to a power level of the RF signal. In some embodiments, generating the RF signal includes generating an RF signal using a power amplifier of an RF transmitter circuit. In some embodiments, generating the RF signal includes generating signal RFOUT using amplifier 110, described above with respect to transmitter circuit 100 and FIG. 1.

At operation 820, an internal node of a power detection circuit is driven to a DC node voltage level. In some embodiments, driving the internal node of a power detection circuit to a DC node voltage level includes dividing an input voltage with a voltage divider. In some embodiments, driving the internal node of a power detection circuit to a DC node voltage level includes driving the internal node of the power detection circuit responsive to a clock signal. In some embodiments, driving the internal node of a power detection circuit to a DC node voltage level includes driving internal node INT1 to the DC node voltage component of voltage VIN, described above with respect to power detection circuit 200 and FIG. 2.

At operation 830, from the DC node voltage level, a first component of an output voltage is generated on an output node of the power detection circuit. In some embodiments, generating the first component of the output voltage includes generating a first DC component of the output voltage. In some embodiments, generating the first component of the output voltage includes tracing the DC node voltage level using a source follower.

In some embodiments, generating the first component of the output voltage includes generating voltage VRF on node 125 using power detection circuit 120, described above with respect to transmitter circuit 100 and FIG. 1. In some embodiments, generating the first component of the output voltage includes generating the first DC component of voltage VRF on output node OUT, described above with respect to power detection circuit 200 and FIG. 2.

At operation 840, the RF signal is received on an input node of the power detection circuit. In some embodiments, receiving the RF signal includes receiving the RF signal with a capacitive element coupled to the input node of the power detection circuit. In some embodiments, receiving the RF signal includes receiving signal RFIN on input node IN, described above with respect to power detection circuit 200 and FIG. 2.

At operation 850, the RF signal is divided to generate a modulation signal on the internal node of the power detection circuit. In some embodiments, dividing the RF signal to generate the modulation signal includes dividing the RF signal responsive to a clock signal. In some embodiments, dividing the RF signal to generate the modulation signal includes dividing the RF signal using one or more devices used to generate the DC node voltage level. In some embodiments, dividing the RF signal to generate the modulation signal includes dividing RF signal RFIN to generate the RF modulation signal component of voltage VIN on internal node INT1, described above with respect to power detection circuit 200 and FIG. 2.

At operation 860, by at least partially rectifying the modulation signal, a second component of the output voltage is generated on the output node. In some embodiments, generating the second component of the output voltage includes generating a second DC component of the output voltage. In some embodiments, generating the second component of the output voltage includes generating the second component of the output voltage in response to a clock signal.

In some embodiments, generating the second component of the output voltage includes generating voltage VRF on node 125 using power detection circuit 120, described above with respect to transmitter circuit 100 and FIG. 1. In some embodiments, generating the second component of the output voltage includes generating the second DC component of output voltage VRF on output node OUT, described above with respect to power detection circuit 200 and FIG. 2.

At operation 870, in some embodiments, a reference voltage is generated on a reference circuit output node. In some embodiments, generating the reference voltage includes generating the reference voltage having a same value as a value of the first component of the output voltage.

In some embodiments, generating the reference voltage includes generating voltage VREF on node 135 using reference voltage generator 130, described above with respect to transmitter circuit 100 and FIG. 1. In some embodiments, generating the reference voltage includes generating voltage VREF on output node REF, described above with respect to reference voltage generator 300 and FIG. 3.

At operation 880, in some embodiments, a comparison voltage is generated based on a difference between the output voltage and the reference voltage. In some embodiments, generating the comparison voltage includes generating the comparison voltage equal to the difference between the output voltage and the reference voltage.

In some embodiments, generating the comparison voltage includes generating voltage VCMP on node 145 using comparator 140, described above with respect to transmitter circuit 100 and FIG. 1. In some embodiments, generating the comparison voltage includes generating voltage VCMP on output node CMPOUT, described above with respect to comparator 400 and FIG. 4.

At operation 890, in some embodiments, a gain of the amplifier is adjusted based on the comparison voltage. In some embodiments, adjusting the gain of the amplifier includes adjusting the amplifier to have a gain sufficient to output an RF signal having a predetermined power level. In some embodiments, adjusting the gain of the amplifier includes adjusting the gain of amplifier 110 to output signal RFOUT having a predetermined power level, described above with respect to transmitter circuit 100 and FIG. 1.

In some embodiments, adjusting the gain of the amplifier includes converting the comparison voltage to a digital signal. In some embodiments, adjusting the gain of the amplifier includes converting voltage VCMP to bits n on signal path 155 using ADC 150, described above with respect to transmitter circuit 100 and FIG. 1.

In some embodiments, adjusting the gain of the amplifier includes converting the comparison voltage to a digital signal by initiating a successive approximation sequence in an ADC. In some embodiments, adjusting the gain of the amplifier includes converting the comparison voltage to a digital signal during a second mode of operation, described above with respect to power detection circuit 200, reference voltage generator 300, and FIGS. 2 and 3.

By executing some or all of the operations of method 800, a power level of an RF signal is detected while obtaining the power and circuit size benefits described above with respect to transmitter circuit 100, power detection circuit 200, reference voltage generator 300, and comparator 400.

In some embodiments, a transmitter circuit includes an amplifier configured to output an RF signal on an output node, a power detection circuit coupled with the output node and configured to generate an output voltage having a first component based on a power level of the RF signal, a reference voltage generator configured to generate a reference voltage, a comparator configured to receive the output voltage and the reference voltage, and an ADC coupled between the comparator and the amplifier. The amplifier is configured to adjust the power level of the RF signal responsive to an output of the ADC.

In some embodiments, a transmitter circuit includes an amplifier configured to output an RF signal on an output node, a power detection circuit coupled with the output node and configured to generate an output voltage based on a power level of the RF signal, and a comparator configured to generate a comparison voltage based on a ground voltage in a first operating mode and based on the output voltage and a reference voltage in a second operating mode. The amplifier is configured to adjust the power level of the RF signal responsive to a digital input based on the comparison voltage.

In some embodiments, a transmitter circuit includes an amplifier configured to output an RF signal on an output node, a power detection circuit coupled with the output node and configured to, in a first operating mode, output a ground voltage, and, in a second operating mode, generate an output voltage having a first component based on a DC bias voltage and a second component based on a power level of the RF signal. The transmitter circuit includes a reference voltage generator configured to output the ground voltage in the first operating mode, and generate a reference voltage based on the bias voltage in the second operating mode, and an ADC configured to generate a plurality of bits based on the ground voltage in the first operating mode, and based on the output voltage and the reference voltage in the second operating mode. The amplifier is configured to adjust the power level of the RF signal responsive to the plurality of bits.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A transmitter circuit comprising: an amplifier configured to output a radio frequency (RF) signal on an output node; a power detection circuit coupled with the output node and configured to generate an output voltage having a first component based on a power level of the RF signal; a reference voltage generator configured to generate a reference voltage; a comparator configured to receive the output voltage and the reference voltage; and an analog-to-digital converter (ADC) coupled between the comparator and the amplifier, wherein the amplifier is configured to adjust the power level of the RF signal responsive to an output of the ADC.
 2. The transmitter circuit of claim 1, wherein the power detection circuit is configured so that the output voltage increases with respect to an increasing amplitude of the RF signal.
 3. The transmitter circuit of claim 1, wherein the comparator is configured to output a comparison voltage based on a difference between the output voltage and the reference voltage.
 4. The transmitter circuit of claim 1, wherein each of the power detection circuit and the reference voltage generator is configured to receive a clock signal.
 5. The transmitter circuit of claim 4, wherein the power detection circuit is configured to: generate the output voltage in response to the clock signal having a first logical value; and generate a ground voltage in response to the clock signal having a second logical value different from the first logical value.
 6. The transmitter circuit of claim 4, wherein the reference voltage generator is configured to: generate the reference voltage in response to the clock signal having a first logical value; and generate a ground voltage in response to the clock signal having a second logical value different from the first logical value.
 7. The transmitter circuit of claim 1, wherein the power detection circuit is configured to generate the output voltage having a second component based on a direct current (DC) bias voltage, and the reference voltage generator is configured to generate the reference voltage based on the DC bias voltage.
 8. The transmitter circuit of claim 7, wherein at least one of the power detection circuit or the comparator is configured to have a sensitivity responsive to the DC bias voltage.
 9. The transmitter circuit of claim 7, wherein the transmitter circuit is configured to receive the DC bias voltage having a value ranging from a threshold voltage of a transistor in the power detection circuit to a power supply voltage.
 10. The transmitter circuit of claim 1, wherein the power detection circuit is configured to generate the output voltage having a second component based on a circuit device arrangement matching a circuit device arrangement of the reference voltage generator.
 11. The transmitter circuit of claim 1, wherein the ADC comprises a successive approximation register (SAR) ADC.
 12. A transmitter circuit comprising: an amplifier configured to output a radio frequency (RF) signal on an output node; a power detection circuit coupled with the output node and configured to generate an output voltage based on a power level of the RF signal; and a comparator configured to generate a comparison voltage based on a ground voltage in a first operating mode and based on the output voltage and a reference voltage in a second operating mode, wherein the amplifier is configured to adjust the power level of the RF signal responsive to a digital input based on the comparison voltage.
 13. The transmitter circuit of claim 12, wherein the transmitter circuit is configured to receive a clock signal, the first operating mode is based on a first logical value of the clock signal, and the second operating mode is based on a second logical value of the clock signal different from the first logical value of the clock signal.
 14. The transmitter circuit of claim 13, wherein the clock signal has a switching frequency ranging from 100 Hertz (Hz) to 1000 Hz.
 15. The transmitter circuit of claim 12, further comprising a reference voltage generator configured to generate the reference voltage, wherein each of the power detection circuit and the reference voltage generator is configured to couple an output node to a ground node in the first operating mode and to couple the output node to a source follower in the second operating mode.
 16. The transmitter circuit of claim 12, wherein the transmitter circuit is configured so that the digital input causes the amplifier to maintain a previous gain level in the first operating mode.
 17. A transmitter circuit comprising: an amplifier configured to output a radio frequency (RF) signal on an output node; a power detection circuit coupled with the output node and configured to in a first operating mode, output a ground voltage, and in a second operating mode, generate an output voltage having a first component based on a direct current (DC) bias voltage and a second component based on a power level of the RF signal; a reference voltage generator configured to output the ground voltage in the first operating mode, and generate a reference voltage based on the bias voltage in the second operating mode; and an analog-to-digital converter (ADC) configured to generate a plurality of bits based on the ground voltage in the first operating mode, and based on the output voltage and the reference voltage in the second operating mode, wherein the amplifier is configured to adjust the power level of the RF signal responsive to the plurality of bits.
 18. The transmitter circuit of claim 17, wherein the transmitter circuit is a component of an RF transmitter having an operating frequency ranging from 2.2 gigahertz (GHz) to 2.6 GHz or from 5.6 GHz to 6.0 GHz.
 19. The transmitter circuit of claim 17, wherein the ADC is configured to generate the plurality of bits having a number ranging from four bits to six bits.
 20. The transmitter circuit of claim 17, wherein the ADC is configured to generate the plurality of bits using a successive approximation register (SAR). 